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질소를 첨가한 316L 스테인리스 강의 고온 저주기 피로균열 생성
김대환,류우석,국익현,김우곤 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.5
The effect of nitrogen on the nucleation of a low cycle fatigue (LCF) crack was studied at high temperature using type 316L stainless steel with different nitrogen contents (0.04-0.15%). Strain-controlled LCF tests were conducted in the temperature range of R.T. ∼600℃ and in air. The waveform of LCF was a symmetrical triangular with a total strain amplitude of 1.0% and in a constant strain rate of 2×10^(-3)/s for all tests. The sites for crack nucleation, crack population, and crack depth from the surface of the specimens were measured after LCF testing up to 40% of fatigue life. The preferred sites for crack nucleation were grain boundaries, but some of cracks also nucleated at twin boundaries and slip bands. Crack population on the surface of the specimen decreased but the maximum depth of the crack from the surface of the specimen did not change with the addition of nitrogen at high temperatures. The cycles for the nucleation (100㎛) of LCF crack increased with the addition of nitrogen. So, the increase of LCF life with the addition of nitrogen at high temperatures may be explained by the fact that nitrogen increases the resistance of crack nucleation.
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Ti-Ni50-x Pdx 합금의 형상기억 특성에 관한 연구
천병선,이희우,오석진,국익현 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.8
The shape memory characteristics in TiNi alloys are greatly effected by the alloy composition and heat treatment condition. The present work was aimed to investigate the effect of Pd_x(X=5, 10, 15, 20) addition on the shape memory characteristics of TiNi alloys by means of eletrical resistance measurement, X-ray diffraction, differential scanning calorimetry and electron dispersive analysis X-ray measurement. The results obtained from this study are as follows ; 1. The martensitic transformation start temperature, Ms of Ti-Ni_(50-x)-Pd_x alloys decreased considerably with the increase of Pd content up to 10at%, whereas increased largely with the increase of Pd content in the alloys with Pd content more than 15at%. 2. The Ms temperature of Ti-Ni_(50-x)-Pd_x alloys with cold working was significantly lower than that, of the fully annealed alloys because high density dislocation has been introduced by the cold working which suppressed the martensitic transformation.
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질소를 첨가한 Type 316L 스테인리스 강의 동적변형시효 거동
김대환,홍준화,최시경,류우석,국익현 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.3
Tensile tests were conducted with varying strain rate (1×10^(-2)/sec∼2×10^(-4)/sec) at the test temperature range between room temperature and 750℃ to evaluate the effect of nitrogen on dynamic strain aging (DSA) behaviors in nitrogen added type 316L stainless steels. Yield and tensile strength increased without reduction of elongation with adding nitrogen. The temperature range and the critical strain for DSA increased with nitrogen addition. Types A and B serrations were observed at 600℃ and the strain for transition from type A to type B increased with nitrogen addition. Solute atoms for DSA were vacancies and chromium and the activation energy for DSA increased with adding nitrogen. The reason that nitrogen retarded DSA was explained by the fact that nitrogen reduced the chromium diffusion to dislocations due to the strong interaction between nitrogen and chromium.
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